1. Field of the Invention
The present invention relates to a multi-functional head for extracting nuclear fuel rods from a spent nuclear fuel assembly. More specifically, the present invention relates to a multi-functional head for extracting spent nuclear fuel rods, in which the rods can be extracted one by one from a Korean type 17xc3x9717 LWR(Light Water Reactor) fuel assembly.
2. Description of the Prior Art
In order to reduce the space for the storage of the spent nuclear fuel assemblies, many countries are developing the rod consolidation technology. The rod consolidation technology is that the fuel rods are extracted from the fuel assembly as shown in FIG. 1 and are contained in separate containers so as to reduce the space for the storage. In this technology, the fuel rod extraction is required, and this is called xe2x80x9cnuclear fuel rod extracting techniquexe2x80x9d. The nuclear fuel rod extracting equipment has been developed by NUS company and BandW company of the United States, and by GNS company of Germany, but it has not been developed in Korea.
The rod extracting equipment consists of the following two functional devices. That is, one of them is a separating device for separating a top end piece(top nozzle) or a bottom end piece(bottom nozzle), and another is a puller for pulling and extracting the nuclear fuel rods by holding the exposed top portion or the bottom portion of the rods after removing top or bottom end pieces.
The top end piece or the bottom end piece is attached in different manners depending on the manufacturing companies.
That is, in one method, the top (or bottom) end piece is welded to a plurality of guide thimbles, while in another method, the top (or bottom) end piece is fastened to a plurality of guide thimbles by means of bolts. In the ones which have been manufactured in foreign countries, it is mostly welded, while in the ones manufactured in Korea, it is bolt-fastened.
In separating the top (or bottom) end piece from the nuclear fuel rod assembly, NUS company of the United States adopts a method in which a plurality of thimbles are simultaneously cut off by inserting a cutting saw into between the top (or bottom) end piece and the end of the nuclear fuel rods. BandW company of the United States and GNS company of Germany adopt a method in which the thimbles are cut one by one by inserting an internal tube cutter into the thimble as deeply as required. Cutting process has inherently a risk of a fire accident, and it produces a lot of debris and/or dust which contaminates the facility. Accordingly, in the present invention, the bolt unfastening method is adopted which is applicable to the Korean type 17xc3x9717 LWR(Light Water Reactor) fuel assembly.
In the case of the puller for extracting the fuel rods after removing the top (or bottom) end piece, NUS company of the United States and GNS company of Germany developed a multiple rods puller in which one row of fuel rods can be extracted simultaneously. Meanwhile, BandW company of the United States developed a single rod puller in which one rod is pulled at each time. In the multiple rods puller, the working time can be shortened very much. But if there are damaged rods in one row, not only the whole row of the rods may not be extracted, but also the additional damages may be inflicted to the rods. In contrast to this, in the single rod puller, the working time is extended, but a safe extraction is realized.
When using the fuel rod puller, the center of the gripper has to be exactly matched with that of the end of the fuel rod. If the gripper advances with the centers misaligned, the gripper is collided with the fuel rod resulting in damage of the fuel rod. Accordingly, before extracting the fuel rods, the coordinates of the centers of all the fuel rods are memorized into a control system, and the gripper is made to advance with the memorized coordinate values, thereby extracting the fuel rods. The coordinates of the centers of the rods are obtained from the design data which has been used for manufacturing the fuel assembly.
Before the burnup, the fuel assembly is manufactured based on the design, and therefore, the ends of all the 17xc3x9717 fuel rods have exact coordinate values. However, during the burnup of the fuel assembly, the fuel rods can be deformed, and their actual coordinate values may be different from the designed values, resulting in the collision of the gripper with the fuel rods during the extraction of the rods.
In this case, the extracting operation is terminated, and the operator manually carries out fine adjustments of the gripper while watching a CCTV, to match the center of the gripper with that of the fuel rod. However, the fine adjustment cannot be easily carried out due to the limited CCTV information. Therefore, the work efficiency is drastically lowered, and the safety is jeopardized.
The present invention is intended to solve the above-described disadvantages of the conventional techniques.
Therefore, it is an object of the present invention to provide a multi-functional head for extracting spent nuclear fuel rods, in which a bolt unfastening function for separating the top (or bottom) end piece, a single rod extracting function, and a localizing function of the fuel rods and the bolts for locating a gripper and a bolt unfastening tool at exact positions.
The apparatus of the present invention is useful for an efficient management of the spent nuclear fuel. In Korea, the electric generation by the nuclear power plants occupies more than 40% of the total electric generation. Therefore, large amounts of spent nuclear fuels are being accumulated. The spent nuclear fuels are temporarily stored in the respective nuclear power plants, and the reracking is being carried out due to the limit of the storage spaces, while the rod consolidation method is being considered. Further, for the peaceful utilization of the potential resources, the DUPIC (Direct Use of PWR fuel In CANDU reactor) process is being developed. In order to develop the nuclear fuel rod extracting technique which is indispensable in all the above described processes, the present inventor invented a multi-functional head for extracting spent nuclear fuel rods.
In the present invention, the head is named xe2x80x9ca multi-functional rotary headxe2x80x9d which consists of: a multi-functional tool part consisting of various tools, sensors and a camera; and a tool rotating part for rotating the above mentioned multi-functional tool part.
The multi-functional tool part consists of: a camera for measuring the positions of the fuel rods and the securing nuts fastened to the top (or bottom) end piece; an impact wrench for unfastening the securing nuts; and a gripper for gripping and pulling the fuel rods. All of these are disposed on the circumference of a rotary disc at intervals of 90 degrees, and the rotary disc is rotated by 90 degrees by driving the tool rotating part. The multi-functional rotary head is movable in the horizontal, lateral, and vertical directions.
The operating sequence of the multi-functional rotary head is as follows. That is, first the positions of all the securing nuts are measured by processing the image obtained by the camera.
By utilizing this position information, the rotary head is moved, so that the impact wrench of the multi-functional tool part would be fitted to the securing nut. The securing nuts are taken out by driving the impact wrench and the top(or bottom) end piece is separated out. The positions of all the fuel rods are measured by utilizing the same method adopted in bolt measurement process. By utilizing the position information, the multi-functional tool part is moved, so that a collet of the gripper can hold the fuel rod. The fuel rod is inserted into the collet, and the collet is closed to grip the end portion of the fuel rod so as to pull out the fuel rod.
To automatize this operating sequence, a means for detecting malfunctions is required.
Particularly if the fuel rod is pushed or pulled by an excessive force, the end portion of fuel rod can be broken causing the contamination of a facility. Therefore, the extraction force for pulling the fuel rods has to be necessarily measured.
Further, whether the fuel rod is accurately inserted into the collet has to be monitored. Accordingly in the present invention, the collet inserting force and a pulling force of the fuel rods are monitored by using the load cell installed at the rear of the collet.
Further, a remote compliance center(RCC) is installed at the rear of the collet, so that the collet would be smoothly inserted onto the fuel rod, even though there exists a small misalignment between the centers of the fuel rod and the collet.